1. Field of the Invention
This invention relates to a process for producing a high concentration coal-water slurry and more particularly it is directed to a controlling process for making uniform the quality of the produced slurry.
2. Description of the Prior Art
Coal has been considered as a petroleum substitute fuel in view of the energy situation in recent years. In order to expand its utilization, research and development directed to various utilization techniques therefor have been vigorously made. Coal, however, has a drawback in that its handling is troublesome due to solids. In order to overcome the drawback, coal-utilizing techniques in the form of slurries have been researched. Their representative examples are a mixed fuel of coal with oil, COM (Coal-Oil-Mixtures), a mixed fuel of coal with water, CWM (Coal-Water-Mixtures), etc. However, the coal conversion of COM is about 50% on the weight basis, whereas that of CWM is 100%; hence the latter has been noted.
CWM which is stable for a long time and whose direct spray combustion is possible, has coal concentrations of about 60% by weight or more, coal particle sizes of 200 meshes (74 .mu.m) pass of about 70 to 80% by weight and slurry viscosities of about 2,000 cp or less. It is possible to produce CWM having such properties by (1) adjusting the particle size distribution of coal particles having a broad width to raise the size packing density of coal particles to thereby make the concentration of the resulting slurry higher, and (2) adding a suitable surfactant and pH adjustor to coal particles to make the particle surface hydrophilic, adjust the surface potential of particles and disperse particles in stabilized manner through repelling of particles against one another to thereby make the viscosity of the resulting slurry lower. This will be described referring to the accompanying drawings. FIG. 13A and 13B illustrate this in a model manner. FIG. 13A illustrates a coal slurry of coal particles 100 having a narrow particle size distribution and FIG. 13B illustrates that having a broad particle size distribution. It is seen that the packing in the case of FIG. 13B is denser than that in the case of FIG. 13A. Further FIG. 14 illustrates a state wherein a surfactant having a hydrophobic group 102 and a hydrophilic group 104 functions upon coal particles 100 to effect making the particles hydrophilic through formation of a water layer and dispersing the particles by means of charge. In order to continuously produce CWM having a uniform quality as fuel, it is indispensable in the apparatus production to always adjust to adequate proportions, the quantity of coal fed, the quantity of water fed, and the quantities of a surfactant and a pH adjustor added. Further, coal is not of a uniform substance, and even in the case of coal mined from the same seam, its properties, particularly grindability and intrinsic moisture vary depending on each lot. Furthermore, even after it is dug, the surface moisture of coal varies depending on environmental changes and its pH varies due to oxidation. Thus, there has been a need for a controlling process capable of continuously producing a CWM having a uniform quality by rapidly corresponding to variations of factors having effects upon such properties of CWM.
The object of the present invention is to provide a controlling process which overcomes the technical problems of production of a high concentration coal-water slurry to thereby make it possible to continuously produce a high concentration coal-water slurry having a uniform quality.